The solar energy, an ideal recycle energy, is a kind of energy source which can be endlessly used and does not produce any pollution. There is still an infinite and marvelous potentialities of applying the solar energy. However, the applied solar energy technique is far from satisfying the requirements of its commercial use.
Research on applying solar energy technique is in progress at various aspects but the common problem that the solar energy density is too low still exits. Even if the sun irradiates in a vertical direction in a fine day, the maximum value of the solar energy density is about 1000 watt/m2 only. This restrains the development of the technology in this field.
The applied non-focusing solar energy technique includes, for example, transforming the sunlight directly into the electrical energy through a solar energy battery. Because the power generation efficiency is about 15% and the cost of manufacturing the solar energy battery is high at present, the peak power of a solar cell panel of 1 m2 is only about 150 watt and the electric energy thus generated is about 200 kw each year, and the unit cost of the electrical energy is ten times of the thermal power generation. Such high cost of manufacturing electricity completely cannot be considered as a purpose for the commercial use.
Besides, the technology of converting directly the solar energy into the heat energy means to transform the solar energy into hot water, hot steam or other hot melt material. Nowadays, the widely used vacuum tube water heaters which utilize the solar energy at lower temperature can only produce hot water at 80 to 90° C. in summer and 40 to 50° C. in winter due to the energy density of the solar energy is too low even the sunlight irradiates the vacuum tube directly. The water with such temperature can only be used for the family showers and not for other purposes.
The key problem of solar utilization is that the solar energy density is too low to be used. Hence, it is a possible way to focus the solar energy by a condenser mirror so as to increase the solar energy density for the subsequent utilization. In recent years, many experts have tried various light collecting devices to solve the problem but all failed. There is no collecting device deserving a commercial use hitherto. The most difficult technical problem to be solved is that the condenser mirror has to follow the sun to obtain a higher solar energy ratio, which no doubt will increase greatly the running cost of the whole system.
In the past, people had made a refraction condenser mirror with refractors, which could be further made into a solar high temperature furnace with plane mirrors, on the basis of the refraction principle. Obviously, the glass mirrors are heavy in weight, the manufacture process is complex and, of course, the cost is very high and then the condenser mirror could not be produced in a large size. Hence, the refraction condenser mirror ceases to get a further development. In 70's of last century, people developed large-scaled planarized Fresnel mirror so as to make a solar collecting heater. The Fresnel mirror is light in weight and costs lower and has functions of point focusing and line focusing. It is typically made of organic glass or other transparent plastic materials or glass. The Fresnel mirror is mainly used for a power generation system with solar battery, but the results are not good.
The popular solar collecting and utilizing devices are all reflector types. These devices include an absorber and a tracking system besides the reflector and are of three types: tank type solar collecting unit, tower type solar collecting unit and disk type solar collecting unit. 1). The tank type solar collecting unit is also called the tank type line-focusing system. The unit uses the parabolic cylinder tank type reflector to focus sunlight on the tube-like collectors to heat the heat transferring working medium in the tube and to obtain the intermediate temperature working medium and then to produce steam in a heat exchanger and thus make a conventional steam turbine running to generate electricity. The unit needs a unidimensional tracking. 2). The tower type solar collecting unit is also called as the tower type focusing system. The basic structure of the unit includes a plurality of heliostats comprising plane reflectors or curved surface reflectors, which track the sun individually. These heliostats reflect and focus the sunlight on a collector fixed on the top of the high tower under the control of a computer. The working medium in the collector may approach to a high temperature and then obtain a great energy. 3). The disk type solar collecting unit also refers to the dish type focusing system or Sterling system. The dish type focusing system consists of paraboloidal reflectors. The receiver is set on the focus of the paraboloid and the heat transferring working medium therein is heated to about 750° C. and thus makes the engine generate electricity. Such systems are capable of approaching to high temperature but also need a two-dimensional tracking.
The above-mentioned three systems share a common defect: the transformation between the light energy and the heat energy is carried out in open air, and the loss of the heat is great. Since the revolution way of each light collecting mirror in the tower type system is different with each other, the control process is complicated and the requirements for the reflection and the tracking precisions are strict, therefore, the costs for design, installation, operation and maintenance are high. Meanwhile, building a high tower occupies a large part of the investment.
The efficiency of the heat transformation of the tank type system becomes low because of the change of focusing. In addition, a tracking equipment needs a reflector with a larger area as well as an oil duct containing intermediate oil for heat transformation. However, the wind proofing and the heavy weight of the equipment itself require a high intensity of the tracking equipment, resulting in a high cost for manufacturing a carrier equipment. Also, the oil for heat transformation makes a part of the investment. Due to the limitation of evaporating temperature of the oil, the resulting evaporating temperature for power generation will be lower as less than 350° C. As a result, the efficiency of power generation is low. Moreover, because the ability of the heat storage in the system is low and the time of the usage of the power equipment is short, the total cost for electricity generation is much higher than that using the conventional energy sources.
The disk system meets the requirements of the generation capacity only when its light collecting mirrors have enough areas, generally larger than 50 square meters, and thus a high wind proofing intensity for the tracking equipment is necessary. In addition, the power generation equipment is also secured on the tracking equipment, resulting in a high cost for manufacturing the tracking equipment. Moreover, the system can only generate electricity during the radiation of the sun and cannot store heat, thus, the efficient utilizing time per year of the system (when in a full load) is less than 2,000 hours. And its total cost for electricity generation is much higher than that using the conventional energy sources.
The table given below shows the main technical and economic parameters for these three systems.
Tower typeTank type systemsystemDisk type systempower (megawatt) 30-32010-20 5-25running temperature390/734 565/1049750/1382(°C.)year capacity factor23%-50%20%-77%25%peak value20%23%29%efficiencyyear net efficiency11%-16% 7%-20%12%-25%Storage conditionlimitedyesBy secondary cellUSD/m2630~275475~2003.100~320  USD/watt4.0~2.74.4~2.512.6~1.3 
In order to resolve the technical problem, different technical solutions have been taken into consideration in the art, e.g., trying to give up the way of using a collecting mirror to track the sun. A Chinese patent No. 96192811.5 discloses a non-tracking line-type solar focusing system with a high efficiency. Instead of positioning the receiver to extend from the focal line to the outwardly extending line of the focal line, in the patent, each end of the focal line of the condenser mirror in the system is provided with a lateral reflect plate which is perpendicular to the focal line and connected to each end of the condenser mirror such that the length of the energy collector and the length of the receiver can be both shortened. In the Chinese patent, the primary solar energy collector adopts the curved surface reflector disclosed in the U.S. Pat. No. 5,289,356, the secondary solar energy collector adopts the curved surface reflecting condenser mirror disclosed in the U.S. Pat. No. 5,274,497; the secondary solar energy collector is located near ½ of the radius of curvature of the primary solar energy collector and disposed with a fluid transport conduit longitudinally. Obviously, such improved technology still needs to keep a precise tracking control system and is equivalent to an ordinary line focusing reflector which converges the solar energy only once and thus fails to increase remarkably the density of the solar energy flowing into the fluid transport conduit. Therefore, the technology only meets the requirements of the small-scaled low temperature ranges (≦200° C.) and has no significant effect in the industrialized energy production. Moreover, if the temperature is very high, the movable connection between the thermal conduits will be a problem.
Contents of the Invention
With regard to the defects existed in the art utilizing solar energy, the technical problems need to be resolved in the present invention are to provide a solar collecting and utilizing device which can enhance highly the solar condensing density, centralize the energy conversion/using point, simplify the solar tracking mechanism, improve the mechanical reliability of the whole system, and lower the investment and the cost of operation.
The technical solution of the present invention relates to a solar collecting and utilizing device. The device comprises: one or more paraboloidal light collecting mirrors for collecting/converging the sunlight; a light guider including a light guider mirror for receiving the sunlight converged by said paraboloidal light collecting mirrors and converting it into parallel light beams in a desired direction; one or more curved surface condenser mirrors for receiving/converging substantially parallel light beams from said light guider; a solar storage and conversion device for storing/converting the energy converged by said curved surface condenser mirrors; a solar tracking equipment for tracking automatically the sunlight so as to always keep the opening surface of said paraboloidal light collecting mirrors substantially vertical to the sunlight. The focus of said light collecting mirror always superposes the focus of the corresponding light guider mirror. Each paraboloidal mirror is fixed with a light guider and the light guiders on many paraboloidal mirror can share a common curved surface condenser mirror. In the latter case, some light guiders on different paraboloidal mirror either permanently share a common curved surface condenser mirror, or alternately share several adjacent curved surface condenser mirrors according to the changes of the daylight, seasons and weathers, etc., which in fact still share a common curved surface condenser mirror. The present invention improves a conventional sunlight collector as a structure containing both light guider and curved surface condenser mirror based on following principle of optics: a mirror capable of point focusing the light can transmit the light located on its focus as a parallel light beam after refraction or reflection. Wherein the light guider is configured to transmit the energy as a light energy and then have the light energy receiving a second convergence through the curved surface condenser mirror. With the improvement, a plurality of light guiders can point at and use a common curved surface condenser mirror, and the curved surface condenser mirror can re-converge the primarily condensed light reflected from a number of paraboloidal mirrors and light guiders. Such secondary or even more multiple stages of solar convergence re-converge in parallel the light having been primarily condensed by the light collecting mirror with large area onto the curved surface condenser mirror through the light guider, and direct the converged light to the relative small and fixed space in the solar storage and conversion device through a secondary re-convergence, so that the convergence density of the solar energy is much higher than that obtained by the conventional disk type or tank type or even tower type of light convergence devices, which makes sure that the absorption or the conversion of the high energy density can be carried out in the solar storage and conversion device. Hence, the solar energy density obtained by the device of the present invention is greatly increased, which assures the final solar receiving and conversing working medium can be heated to the desired high temperature. Moreover, the high level convergence can heat the energy receiving medium to a high temperature and help realize the high temperature preserving, and then increase the year average working hours of the equipment using the generated heat energy, meanwhile lower the cost of manufacturing the whole system. Further advantages of the device of the present invention show that: transferring the primarily condensed energy as the type of the solar energy can greatly decrease the complexity, the expense and the consumption of transferring energy during the process of the energy convergence, compared to the conventional transferring technique using the melted mass, gas, fluid, wires, etc.; instead of setting up the solar storage and conversion device on a high tower as the conventional tower type solar collecting device did, the present solar storage and conversion device for transferring/using the solar energy can be built on the ground not on a tower, and the primary light collecting, secondary transferring and the following solar energy convergence can all be carried out on the ground, which result in that the investment and the cost for maintaining the system become much lower; it is easier to aim a plurality of solar collecting mirrors at the curved surface condenser mirror through the guider mirror, and the requirement for the tracking precision is low, thus a single tracking equipment is capable of controlling multiple solar collecting mirrors at the same time and it is also possible for the multiple solar collecting mirrors to track synchronously the sunlight, which largely simplifies the control system compared to the conventional tower type collecting device with multi-mirror and multi-dimension tracking equipment; the solar storage and conversion device is set up on the ground not on the light collecting mirror, and the implementing mechanical parts of the tracking equipment have no need to load the solar storage and conversion device as well as the working medium therein, which lower the requirement for the work intensity of the implementing mechanical parts in the tracking equipment. Hence, the reliability of the mechanism of the whole system and the sunlight tracking equipment is dramatically enhanced, meanwhile, the maintenance is convenient and the operation control is simple, so as to meet requirements of the large scaled industries.
The light guider employed in the embodiment of the present invention is a concave mirror capable of focusing light or a combination of mirrors and lens consisting of convex lens and plane reflector, wherein, the focus of the concave mirror or the convex lens superposes the focus of said paraboloidal light collecting mirror. The condenser mirror of the present invention may also be any type of optical system capable of focusing the light, more particularly, said optical system can transmit the light located on its focus as a parallel light beam after refraction or reflection. Therefore, said condenser mirror is not limited to the type and structure mentioned in the above embodiment.
In order to obtain the potential high solar concentrating density, the light collecting area of the paraboloidal mirror shadowed by the light guider must be limited to the least. Meanwhile, in order to minimize the scattering angle and maximize the range of the parallel light beam transmitted from the light guider, and maximize the number of the paraboloidal mirror and/or the light guider arranged without interference and shadow in arrays, the ratio of the solar shadow area of a light guider on a light collecting mirror to the area of the mirror opening of said light collecting mirror is less than 1.5%, and the ratio of the solar shadow area of a guider mirror on a paraboloidal mirror to the area of the mirror opening of said light collecting mirror is between 0.1%-1.5%, on the basis of the specific theoretical calculation and trials in the present invention. Correspondingly, when the paraboloidal mirror is surely capable of condensing the light, the desired paraboloidal mirror and/or the guider mirror and/or the curved surface condenser mirror are intact paraboloidal rotation type of reflection condenser mirror, or the effective parts of the paraboloid rotation surface type of the reflection condenser mirror, e.g., the arc part, the fan shaped part, the left curved surface part after the arc part is cut, the left curved surface part after the fan shaped part is cut or the half curved surface. Moreover, the ratio of the focal distance of the light collecting mirror to its mirror opening diameter is between 0.55-1.1, and the ratio of the focal distance of the guider mirror to its mirror opening diameter is between 0.1-0.3. Further, the paraboloidal mirror and/or the curved surface condenser mirror of the present invention may also adopt a complete reflection condenser mirror with asymmetrical curved surface or its effective cut parts.
To fully realize the simplification of the solar tracking equipment and the advantages of the device, the device of the present invention can be configured as a kind of array system. In the embodiments of the present invention, the mirror axes of a number of curved surface condenser mirrors are set in the direction of south to north and arranged in juxtaposition in the direction of east to west; the mirror axes of a number of guider mirrors are also set in the direction of south to north and point at arrays of curved surface condenser mirror groups horizontally; a plurality of light collecting mirrors in arrays are correspondingly set in same height in the direction of south to north and are arranged linearly in same height in the direction of east to west, and guider mirrors at different distances pointing at a same curved surface condenser mirror are arranged in a way of non-interference horizontally, or a plurality of light collecting mirrors in arrays are correspondingly set linearly in the direction of south to north and are arranged linearly in same height in the direction of east to west, and guider mirrors at different distances pointing at a same curved surface condenser mirror are arranged in a way of non-interference by stepping up. To realize simplifying the solar tracking equipment, the curved surface condenser mirror can be arranged in other array types, e.g., diamond, trapezoid, triangle, etc., according to different landforms and conditions where the device of the present invention is fixed. In conclusion, a plurality of light collecting mirrors corresponding to a same curved surface condenser mirror in the device of the present invention can be arranged in array groups, a single array group of condenser mirror is capable of converging the sunlight of more than scores of square meters. After search and investigation, it is proved that current techniques of manufacturing optical reflector can meet all the requirements of producing the parts of the device of the present invention. Meanwhile, once the device of the present invention is widely used in industry, the focus precision of the optical reflector will get further improved on the basis of the fact that the optical film deposit technique has been digitalized and the cost of manufacturing the device of the present invention will be greatly lowered. According to a rough estimation, when the device is used in a large-scaled industry, the cost will be a bit higher than building up a firepower station, but the maintenance and the operation cost will be lower than an ordinary power station. The composite cost is hopefully near or lower than the cost used for an ordinary power station. If the process of manufacturing a reflector and the techniques of building and operating the system is improved, collecting area of a single group can be further increased. Because the vapour can be decomposed into H2 and O2 at 3000 K, the system has a prospect of producing H2 from water and hopefully it can alter basic energy structure of human being, thereby obtaining a clean energy.
At present, the material machining technique is mature, and the raw material, process and the precision all can meet the requirements of processing a paraboloid mirror, and the optical film deposit techniques develops rapidly at the same time. Therefore, the existing techniques can produce the reflector with the reflectivity over 99%, and the revolving curved surface reflector, such as, the paraboloid, can be produced in a short time with support of the conventional technology. Moreover, the conventional techniques can ensure the installation of the system on the spot.
The implementing mechanical parts in the simplified tracking system employed in the embodiment of the present invention comprise: a power supplying device, a rigid straight-bar driver, and a elevation angle control mechanism of the mirror opening of each paraboloidal mirror, wherein, the rigid straight-bar driver couples simultaneously the elevation angle control mechanism of the mirror opening of each paraboloidal mirror arranged in the same array. Said implementing mechanical parts further comprise a hydraulic driver and visual angle control hydraulic poles of the mirror opening of each paraboloidal mirror, wherein, a hydraulic driver individually connects to the visual angle control hydraulic pole of the mirror opening of each paraboloidal mirror arranged in the same array. Since a plurality of light collecting mirrors are arranged in a straight line south to north and/or east to west, said tracking equipment is configured to use a straight-bar driver, such as a straight rack, to control simultaneously the elevation angle control bevel gears of the mirror openings of each paraboloidal mirror arranged in a same line or a same array. Also, the straight-bar driver and the elevation angle control mechanism of the mirror opening can be communicated by a hydraulic connection device, through which, 5 to 50 paraboloidal mirrors arranged on the same line can use a common set of implementing mechanical parts and photoelectrical control parts of the present invention. As a result, the size and the complexity of the software and hardware of the solar tracking equipment will be greatly decreased but the reliability will be increased instead, and the cost for the system operation and the maintenance will lower to a possible extent.
The light guider of the present invention is hinged to the guider support, the lower part of said guider support is secured to the light collecting mirror or the mirror basket; said light guider comprises a rotation axis in a direction of east to west, a mirror bracket which is hinged to the guider support by said rotation axis, and a rotation mechanism which drives said mirror bracket to rotate about said rotation axis; said mirror bracket is configured and sized to have the focus of the guider mirror superposing the focus of the light collecting mirror. More specifically, the mirror bracket is fixed on two ends of the paraboloidal guider mirror which is cut into the shape of a longbow and forms a “Π” shape. Both arms of said “Π” have axle hole matching the rotation axis and the central line of said axle hole passes the overlapped focus of the light collecting mirror and the guider mirror so as to keep the focus of the guider mirror superposing the focus of the light collecting mirror whatever the depression/elevation angle of the mirror opening changes. And in practice, the mirror axis of the guider mirror basically points at the mirror opening of a certain curved surface condenser mirror horizontally. Correspondingly, the photoelectrical control parts of the present invention connect and control a plurality of straight-bar drivers, hydraulic drivers and rotation mechanism. Such configuration helps to realize that the automatic fine tuning light guider highly aims at the paraboloidal mirror and the curved surface condenser mirror with high efficiency and low cost. Since the movement course of the sun has been clearly understood, the systematic error can be effectively controlled with the precise feedback in the implementing mechanism of the tracking equipment under the control of the computer technology, which keeps the tracking equipment running with high precision and meeting the requirements of the system.
In order to increase the beam collection extent of the light guider and decrease the scattering of the beam caused by the poor quality of the mirror surface, the light guider composed of reflector according to the present invention further comprises a convex lens ring disposed between the light collecting mirror and the guider mirror and/or a concave lens ring disposed between the guider mirror and the curved surface mirror. Thus, the scattered beam at a larger deviation angle transmitted onto the guider mirror or sent out to the curved surface condenser mirror can be corrected parallel to the desired direction.
The device of the present invention uses solar energy of high temperature, then the employed solar storage and conversion device is configured as a multi-layer heat preservation structure. Said structure corresponds to multiple curved surface mirrors and has a light receiving hole with diameter a little larger than that of the focal spot of the curved surface mirror, and said light receiving hole receives the condensed light from the curved surface mirror. Moreover, said device contains a working medium for storing and/or transferring energy in its deepmost; said working medium for storing and/or transferring energy includes melted salt, water, steam, and raw smelt material or photoelectric cell. The above mentioned structure is similar to a black body structure and is helpful to preserve the heat and then various energy sources can be adopted for using the condensed solar energy.
Each curved surface condenser mirror converges the sunlight collected from a plurality of light collecting mirrors, so the largest resulting light collecting area may reach scores of square meters. Research has showed that the vapour can be decomposed into H2 and O2 at 3000 K. If the light with a high convergence ratio in the present system can heat the high temperature resistant medium to over 3000K, the vapour will be conducted into the medium and be heated to the decomposing temperature. It means that when the heat energy is in use, a mass of H2 can be produced. The hydrogen energy is an energy source of high quality and can be reserved steadily and the critical pressure is low and is easy to be fluidified. With the advantage, the application of the present system will have a much wider prospect in the future.